4.1 The test method was developed for determining the fracture resistance of asphalt mixtures. The fracture resistance can help differentiate asphalt mixtures whose service life might be compromised by cracking. The test method is generally valid for specimens that are tested at temperatures of 10 °C or below (see Note 1). The specimen geometry is readily adapted to 150 mm diameter specimens, such as fabricated from Superpave (trademark) gyratory compactors (Test Method D6925), which are used for the asphalt mixture design process. The specimen geometry can also be adapted for forensic investigations using field cores of pavements where thin lifts are present. This geometry has been found to produce satisfactory results for asphalt mixtures with nominal maximum aggregates size ranging from 4.75 to 19 mm (2).

Note 1: The stiffness of the asphalt binder tends to influence the assessment of a valid test as described in 7.4. For instance, a soft asphalt binder which may be required for a very cold climate might not lead to a mixture that would produce valid results at +10 °C and, conversely, a hard asphalt binder utilized in hot climates may require higher temperatures to provide any meaningful information.

Note 2: The quality of the results produced by this test method are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of Specification D3666 are generally considered capable of competent and objective testing, sampling, inspection, etc. Users of this test method are cautioned that compliance with Specification D3666 alone does not completely ensure reliable results. Reliable results may depend on many factors; following the suggestions of Specification D3666 or some similar acceptable guidelines provides a means of evaluating and controlling some of those factors.

Note 3: The failure mechanism experienced in this test is influenced by the aggregate type due to the interactive effect of asphalt binder stiffness and aggregate quality on the fracture path and, therefore, fracture energy values. At high values of asphalt binder stiffness, similar to those experienced near the low-temperature performance grade of the asphalt binder, the crack will travel around the aggregate when the mixture includes hard, non-absorptive (for example, granite, trap rock) aggregates resulting in a longer crack path and higher values of fracture energy. For softer, more absorptive aggregates, the crack will travel through the aggregate, shortening the crack path and leading to lower values of fracture energy (3). Due to the influence of aggregate type on fracture energy, mixture design and/or binder grade adjustments in mixes that use softer aggregates may not be sufficient in improving fracture energy to meet a target value.